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Torque g-cm

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Marks256

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I am going to order a gear box from jameco's robot store. This was explained to me before, but i pretty much forgot.

What is a g-cm?

When my shop teacher explained it to me, he said something about if the torque of a motor was 10-2, the motor could lift 10grams 2cm in 1 minute(which would be simplified to 5grams 1cm in 30seconds). Is that right?

Here is the link to the motor/gearbox i am thinking of getting. I just want to know how powerful it is.

**broken link removed**

So, i if i am right, at the gear ratio of 203:1, the gear box could lift 941grams 1cm in 1minute. Right?
 
That's BS.

If you take a shaft, put a 1cm lever on the end of it and attach a 1gm mass to the end the force excerted on the shaft will be 1gm-cm.

This isn't an SI unit, real engineers specifiy torque in Newtons per meter (Nm).
 
Torque is measured by all sorts of metrics, usually application specific. A common U.S. measurement is pound feet, or on a smaller scale ounce inches. If your motor can produce 10 g/c's of force it's 10 grams of force at 1 centimeter from the center of rotation. Or 1 gram at 10 centimeters. Aside from frictional losses, a motor that can produce 10 g/cm's of force if fed into a gear reducer that is 10-1 will produce 100 g/cm. Most torques are listed as stall torques not in motion, which is significantly more complicated due to the mass and velocity of the various rotating gears.
 
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I know it isn't an SI unit. Ok, so how powerful is that motor/gear box setup thing then?
 
The motor is 4.6 g/cm
The gearbox is 58 to 1 or 203 to 1
The stats are right there on the page.
269 g/cm for low (58:1) and 941 g/cm for high (203:1)
If you think about it for a second it's pretty easy. At 1 centimeter distance it can resist an applied force (IE dead stop) up to 269gms on low and 941 on high, at 1centimeter. So if you put a weight of 1 kilogram at a distance of 1 centimeter it should just about hold it up.
 
Yes, i know the stats were on the page. I wan to know if 941g-cm is pretty powerful? (However, i saw the planetary gearbox on the site, and it has 6000+ g-cm of torque...)
 
Marks256 said:
I wan to know if 941g-cm is pretty powerful?

It all depends on what you want it to do.
You need to calculate how much torque you need to do the job want done and then decide.

It would be like me telling someone "you should use an engine like the one in my car, that has a lot of torque", ony to find that he was trying to power a 40tonne lorry (18 wheeler to you) with it. It would be a bit slow up the hills!!!.

JimB
 
I am going to build a small robot. It will be carrying a motherboard, hard drive, batteries(not sure how heavy, i will weigh them later today after homework), 2 USB web cams, and probably some mounting hardware.
 
Marks256 said:
I am going to build a small robot. It will be carrying a motherboard, hard drive, batteries(not sure how heavy, i will weigh them later today after homework), 2 USB web cams, and probably some mounting hardware.

And you call it "small"?.
 
Sounds like a PC tower on wheels. Might I suggest a Laptop instead? That way, you can also have the screen as a giant smiley face that shows moods, etc. I dunno. hehe.

I have a tutorial about this kind of thing on the forum:
https://www.electro-tech-online.com/threads/motor-sizing-for-moving-robots.23264/

In your case, it sounds like flat ground only. So you can use a coefficient of rolling friction around 0.05 or something. 0.1 is very convservative. You can carry a ridiculous amount of weight on wheels if the ground and wheels are hard, but so there is still enough friction between the two (none of the gummy super grip deformable tire wheels).
 
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It's pretty easy to get a 'feeling' for the amount of torque I'd use 10 centimeters just because it's a little more human scale. Place a 94.1 weight on a rod that is 10 centimeters long connected to another rod at 90degree to it and hold onto this 'axle'. 94.1 grams is 3.3 ounces so find something (a candy bar) or some other food item that weighs 3 ounces and you'll feel what 941 g/cm's feels like to a wheel.

------------ 'axle'
|
|
|
(Load)
 
Dknguyen said:
Sounds like a PC tower on wheels. Might I suggest a Laptop instead? That way, you can also have the screen as a giant smiley face that shows moods, etc. I dunno. hehe.

I did consider this, but then i ran into a problem. Sure, the size, the batteries, ect would be nice, but i wouldn't be able to interface the buses easily. I want to be able to interface the ISA slots for more I/O controls.




Just out of curiosity, are there any robot competitions here in the U.S. and/or Canada(OTHER THAN Battle Bots :) )?
 
There are various sumo competitions, the firefighting competitions like the one from Trinity, other combat robot competitions, F.I.R.S.T., the aerial UAV competitions like AUVSI or UVS Canada, Grand Darpa Challenge, and it goes on and on.
 
Hmm, the DARPA challenge would be fun to enter....
 
this unit means, that the motor can lift a weight of x grams from a distance from 1 cm.
if you connect a 1,5 cm arm to the motors shaft. and connect a load of 1g to the distance of 1cm from the center of the motors shaft then the torque is 1g/cm if it is the max load it can move. if it can move 50g on that shaft the power is 50g/cm. and 25g/2cm etc...
you can also let google or wikipedia explain it to you if you still don't get it
(I'm sorry if you already do... didn't have the time to read every word in the topic here... sorry)
 
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